Chemical mechanical polishing compositions and methods relating thereto

ABSTRACT

The present invention provides an aqueous composition useful for polishing nonferrous metal interconnects on a semiconductor wafer comprising oxidizer, inhibitor for a nonferrous metal, complexing agent for the nonferrous metal, modified cellulose, 0.01 to 5% by weight copolymer of acrylic acid and methacrylic acid, and balance water, wherein the copolymer of acrylic acid and methacrylic acid has a monomer ratio (acrylic acid/methacrylic acid) in the range of 1:30 to 30:1 and the copolymer has a molecular weight in the range of 1K to 1000K.

BACKGROUND OF THE INVENTION

The invention relates to chemical mechanical planarization (CMP) ofsemiconductor wafer materials and, more particularly, to CMPcompositions and methods for polishing metal interconnects onsemiconductor wafers in the presence of dielectrics and barriermaterials.

Typically, a semiconductor wafer is a wafer of silicon with a dielectriclayer containing multiple trenches arranged to form a pattern forcircuit interconnects within the dielectric layer. The patternarrangements usually have a damascene structure or dual damascenestructure. A barrier layer covers the patterned dielectric layer and ametal layer covers the barrier layer. The metal layer has at leastsufficient thickness to fill the patterned trenches with metal to formcircuit interconnects.

CMP processes often include multiple polishing steps. For example, afirst step removes excess interconnect metals, such as copper at aninitial high rate. After the first step removal, a second step polishingcan remove metal that remains on the barrier layer outside of the metalinterconnects. Subsequent polishing removes the barrier from anunderlying dielectric layer of a semiconductor wafer to provide a planarpolished surface on the dielectric layer and the metal interconnects.

The metal in a trench or trough on the semiconductor substrate providesa metal line forming a metal circuit. One of the problems to be overcomeis that the polishing operation tends to remove metal from each trenchor trough, causing recessed dishing of such metal. Dishing isundesirable as it causes variations in the critical dimensions of themetal circuit. To reduce dishing, polishing is performed at a lowerpolishing pressure. However, merely reducing the polishing pressurewould require that polishing continue for a lengthened duration.However, dishing would continue to be produced for the entire lengthenedduration. What is needed is a method to reduce dishing of metal intrenches or troughs without lengthening the duration of the polishingoperation. Polishing compositions that leave a surface clear ofinterconnect metal residue after a short second step polishing time areneeded.

U.S. Pat. No. 6,632,259 describes the use of engineered copolymers inaqueous polishing compositions for CMP. These include copolymers derivedfrom a mixture comprising acrylic acid monomer and methacrylic acidmonomer at a mole ratio of acrylic acid monomer to methacrylic acidmonomer of about 1:20 to about 20:1. These are disclosed in polishingcompositions that do not comprise a modified cellulose.

STATEMENT OF THE INVENTION

In a first aspect, the present invention provides an aqueous compositionuseful for CMP of a semiconductor wafer containing a metal comprisingoxidizer, inhibitor for a nonferrous metal, complexing agent for thenonferrous metal, modified cellulose, 0.01 to 5% by weight copolymer ofacrylic acid and methacrylic acid, and balance water, wherein thecopolymer of acrylic acid and methacrylic acid has a monomer ratio(acrylic acid/methacrylic acid) in the range of 1:30 to 30:1 and thecopolymer has a molecular weight in the range of 1K to 1000K. Thepolishing composition may optionally contain an abrasive at up to 3percent by weight.

In a second aspect, the present invention provides a method for CMP of asemiconductor wafer containing a metal comprising, a) contacting thewafer with a polishing composition, the polishing composition comprisingoxidizer, inhibitor for a nonferrous metal, complexing agent for thenonferrous metal, modified cellulose, 0.01 to 5% by weight copolymer ofacrylic acid and methacrylic acid, and balance water, wherein thecopolymer of acrylic acid and methacrylic acid has a monomer ratio(acrylic acid/methacrylic acid) in the range of 1:30 to 30:1 and thecopolymer has a molecular weight in the range of 1K to 1000K and b)polishing the wafer with a polishing pad. The polishing composition mayoptionally contain an abrasive at up to 3 percent by weight.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graphical description of clear time.

DETAILED DESCRIPTION

The composition and method provide good metal removal rates and adequatemetal clearing without excessive dishing of the metal interconnects whena semiconductor wafer is exposed to CMP. The composition of the presentinvention utilizes water soluble copolymers of acrylic acid andmethacrylic acid along with water soluble cellulose modified withcarboxylic acid functionality. Although the present invention hasparticular usefulness in copper interconnects, the present aqueouspolishing composition also provides enhanced polishing of othernonferrous metal interconnects, such as aluminum, gold, nickel, platinumgroup metals, silver, tungsten, and alloys thereof.

The copolymer of this invention is synthesized utilizing acrylic acidmonomer and methacrylic acid monomer at a mole ratio in a range of 1:30to 30:1; preferably in a range of 1:9 to 9:1; and most preferably about2:3. The copolymer of this invention has a molecular weight in the rangeof 1K to 1000K; preferably in the range of 20K to 200K. For purposes ofthis specification, molecular weight refers to weight average molecularweight.

The polishing composition of this invention contains water solublecellulose modified with carboxylic acid functionality. Preferably, thecomposition contains 0.01 to 5.0 weight percent of water solublecellulose. Most preferably, the composition contains about 0.3 weightpercent of water soluble cellulose. Exemplary modified cellulose areanionic gums such as agar gum, arabic gum, ghatti gum, karaya gum, guargum, pectin, locust bean gum, tragacanth gums, tamarind gum, carrageenangum, and xantham gum, modified starch, alginic acid, mannuronic acid,guluronic acid, and their modifications and combinations. The preferredwater soluble cellulose, carboxy methyl cellulose (CMC), has a degree ofsubstitution of 0.1 to 3.0 with a molecular weight of 1K to 1000K. Morepreferred CMC has a degree of substitution of 0.7 to 1.2 with amolecular weight of 40K to 250K. Degree of substitution in CMC is thenumber of hydroxyl groups on each anhydroglucose unit in the cellulosemolecule that is substituted. It can be considered as a measure of the“density” of carboxylic acid groups in the CMC.

Preferably, the solution contains up to 25 weight percent oxidizer. Morepreferably, the oxidizer is in the range of 5 to 10 weight percent. Theoxidizer is particularly effective at assisting the solution in removingcopper at low pH ranges. The oxidizing agent can be at least one of anumber of oxidizing compounds, such as hydrogen peroxide (H₂O₂),monopersulfates, iodates, magnesium perphthalate, peracetic acid andother per-acids, persulfates, bromates, periodates, nitrates, ironsalts, cerium salts, Mn (III), Mn (IV) and Mn (VI) salts, silver salts,copper salts, chromium salts, cobalt salts, halogens, hypochlorites anda mixture thereof. Furthermore, it is often advantageous to use amixture of oxidizer compounds. When the polishing slurry contains anunstable oxidizing agent such as, hydrogen peroxide, it is often mostadvantageous to mix the oxidizer into the composition at the point ofuse.

Further, the solution contains inhibitor to control copper interconnectremoval rate by static etch or other removal mechanism. Adjusting theconcentration of an inhibitor adjusts the interconnect metal removalrate by protecting the metal from static etch. Preferably, the solutioncontains 0.05 to 5.0 weight percent inhibitor. Most preferably, thesolution contains 0.2 to 1.0 weight percent inhibitor. The inhibitor mayconsist of a mixture of inhibitors. Azole inhibitors are particularlyeffective for copper and silver interconnects. Typical azole inhibitorsinclude benzotriazole (BTA), mercaptobenzothiazole (MBT), tolytriazole(TTA) and imidazole. BTA is a particularly effective inhibitor forcopper and silver.

In addition to the inhibitor, the composition preferably containscomplexing agent for the nonferrous metal. The complexing agent mayfacilitate the removal rate of the metal film, such as copper.Preferably, the composition contains 0.01 to 15 weight percentcomplexing agent for the nonferrous metal. Most preferably, thecomposition contains 0.1 to 1 weight percent complexing agent for thenonferrous metal. Example complexing agents include acetic acid, citricacid, ethyl acetoacetate, glycolic acid, lactic acid, malic acid, oxalicacid, salicylic acid, sodium diethyl dithiocarbamate, succinic acid,tartaric acid, thioglycolic acid, glycine, alanine, aspartic acid,ethylene diamine, trimethyl diamine, malonic acid, gluteric acid,3-hydroxybutyric acid, propionic acid, phthalic acid, isophthalic acid,3-hydroxy salicylic acid, 3,5-dihydroxy salicylic acid, gallic acid,gluconic acid, pyrocatechol, pyrogallol, tannic acid, including saltsand mixtures thereof Preferably, the complexing agent is selected fromthe group consisting of acetic acid, citric acid, ethyl acetoacetate,glycolic acid, lactic acid, malic acid, oxalic acid and mixturesthereof. Most preferably, the complexing agent is malic acid.

The compounds provide efficacy over a broad pH range in solutionscontaining a balance of water. This solution's useful pH range extendsfrom at least 2 to 5. In addition, the solution preferably relies upon abalance of deionized water to limit incidental impurities. The pH of thepolishing fluid of this invention is preferably from 2.5 to 4.2, morepreferably a pH of 2.6 to 3.8. The acids used to adjust the pH of thecomposition of this invention are, for example, nitric acid, sulfuricacid, hydrochloric acid, phosphoric acid and the like. Exemplary basesused to adjust the pH of the composition of this invention are, forexample, ammonium hydroxide and potassium hydroxide.

Further, the polishing composition may optionally contain up to 3 weightpercent abrasive to facilitate metal layer removal. Within this range,it is desirable to have the abrasive present in an amount of less thanor equal to 1 weight percent. Most preferably, the polishingcompositions of the present invention are abrasive free.

The abrasive has an average particle size of less than or equal to 500nanometers (nm) for preventing excessive metal dishing, dielectricerosion and improving planarization. For purposes of this specification,particle size refers to the average particle size of the abrasive. Morepreferably, it is desirable to use a colloidal abrasive having anaverage particle size of less than or equal to 100 nm. Further,decreased dielectric erosion and metal dishing occur with colloidalsilica having an average particle size of less than or equal to 70 nm.In addition, the preferred colloidal abrasive may include additives,such as dispersants, surfactants, buffers, and biocides to improve thestability of the colloidal abrasive. One such colloidal abrasive iscolloidal silica from Clariant S. A., of Puteaux, France. Also, otherabrasives, including, those that are fumed, precipitated, agglomerated,etc., may be utilized.

The polishing composition may include the abrasive for “mechanical”removal of metal interconnect layers. Example abrasives includeinorganic oxides, inorganic hydroxides, inorganic hydroxide oxides,metal borides, metal carbides, metal nitrides, polymer particles andmixtures comprising at least one of the foregoing. Suitable inorganicoxides include, for example, silica (SiO₂), alumina (Al₂O₃), zirconia(ZrO₂), ceria (CeO₂), manganese oxide (MnO₂), titanium oxide (TiO₂) orcombinations comprising at least one of the foregoing oxides. Suitableinorganic hydroxide oxides include, for example, aluminum hydroxideoxide (“boehmite”). Modified forms of these inorganic oxides, such as,organic polymer-coated inorganic oxide particles and inorganic coatedparticles may also be utilized if desired. Suitable metal carbides,boride and nitrides include, for example, silicon carbide, siliconnitride, silicon carbonitride (SiCN), boron carbide, tungsten carbide,zirconium carbide, aluminum boride, tantalum carbide, titanium carbide,or combinations comprising at least one of the foregoing metal carbides,boride and nitrides. Diamond may also be utilized as an abrasive ifdesired. Alternative abrasives also include polymeric particles, coatedpolymeric particles, and surfactant stabilized particles. The preferredabrasive, if utilized, is silica.

The composition of the present invention is applicable to anysemiconductor wafer containing a conductive metal, such as copper,aluminum, tungsten, platinum, palladium, gold, or iridium; a barrier orliner film, such as tantalum, tantalum nitride, titanium, or titaniumnitride; and an underlying dielectric layer. For purposes of thespecification, the term dielectric refers to a semi-conducting materialof dielectric constant, k, which includes low-k and ultra-low kdielectric materials. The composition and method are excellent forpreventing erosion of multiple wafer constituents, for example, porousand nonporous low-k dielectrics, organic and inorganic low-kdielectrics, organic silicate glasses (OSG), fluorosilicate glass (FSG),carbon doped oxide (CDO), tetraethylorthosilicate (TEOS) and a silicaderived from TEOS. The compositions of this invention may also be usedfor ECMP (Electrochemical Mechanical Polishing).

EXAMPLES

To make high molecular weight (˜200,000 MW) AA/MAA 2:3 by mole)copolymer use 75 g AA 100% acrylic acid, 135 g MAA 100% methacrylicacid, 0.5 g+1.9 g NaPS Na₂S₂O₈, MW=238.1, 270 g+42 g+380 g DI water, 20g 50% NaOH. 25 g of mixed monomers is charged to a 4-neck 2000 mlreactor followed by 270 g of DI water and 0.5 g of sodium persulfate.The mixture is heated up to 92° C. then the rest of mixed monomers andthe solution of 1.9 g of sodium persulfate in 42 g of water are co-fedto the reactor for 40 and 50 minutes. The reaction mixture is held foranother 1 hr at 92° C. then let cool to room temperature. GC and GPC ofcrude product are checked and 10% acid is neutralized by 50% NaOHsolution. This procedure gives Mw/Mn=198,000/30,000, AA=532 ppm, MAA=38ppm, pH=3.7, % solid of the crude product is 45.6%. 20 g of 50% NaOH and380 g of water is used to dilute crude product to 24.45%, 800 g of crudeproduct is diluted further to 10% solution.

To make a low MW (˜27,000) AA/MAA (2:3 by mole) copolymer use 179 g AA(100% acrylic acid), 321 g MAA (100% methacrylic acid), 23.4 g NaPS(Na₂S₂O₈), 815 g+110 g DI water, and 49.7 g 50% NaOH solution. 25 g ofmixed monomers is charged to a 4-necked 2000 ml reactor followed by 815g of DI water and 2.4 g of sodium persulfate. The mixture is heated to95° C. then the rest of mixed monomers and the solution of 21 g ofsodium persulfate in 110 g of water are co-fed to the reactor for 140and 160 minutes, respectively. The reaction mixture is held for another1 hr at 92° C. then let cool to room temperature. 49.7 g of 50% NaOH isused to neutralize 10% acid. This procedure gives Mw/Mn=30860/6656, AA=0ppm, MAA=47 ppm, pH=1.2. 49.7 g of 50% NaOH is used to neutralize thecrude product to pH=3.6. Final % solids=37.8%.

In the Example all compositions contain, by weight percent, 0.50 BTA,0.22 malic acid, 0.32 carboxymethylcellulose (CMC), and 9.00 hydrogenperoxide at a pH of 2.8.

The experiment measured copper polishing rates and determined theclearing of residual copper from a semiconductor wafer at a moderatedown force pressure. In particular, the test determined the effect ofthe utilization of modified cellulose compounds in the presence ofcopolymers of acrylic acid and methacrylic acid on the polishing rate,clear time, and residual copper clearing. Clear time is defined asEPD2-EPD1, where EPD1 is the initial endpoint detection time at whichthe first sign of barrier layer is detected through the copper layer.EPD2 is the detection time at which the detector sees only barrierlayer. FIG. 1 graphically shows this definition of clear time. AnApplied Materials, Inc. Mirra 200 mm polishing machine equipped with anISRM detector system using an IC1010™ polyurethane polishing pad (Rohmand Haas Electronic Materials CMP Inc.) under downforce conditions ofabout 2 psi (13.8 kPa), a polishing solution flow rate of 150 cc/min, aplaten speed of 80 RPM, and a carrier speed of 40 RPM planarized thesamples. The polishing solutions had a pH adjusted with nitric acid. Allsolutions contained deionized water.

TABLE 1 Av. Clear Dishing Time Molecular Conc. Residual (A) EPD2 −Slurry aa:maa Weight Wt % RR A/min Clearing 90%/100 um EPD1 1 3:2 0.12755 No 637/463 18 2 1:1 0.1 2119 No 335/341 25 3 2:3  22K 0.05 1496 No358/426 23 4 2:3  27K 0.1 2426 Yes 418/397 27 5 2:3  22K 0.5 1419 No428/411 25 6 2:3 200K 0.1 3172 Yes 642/754 19 7 1:4 0.1 1821 No 363/45725 8 1:9 0.1 1822 No 243/441 26 9 0:1 0.1 1640 No 305/445 21

As illustrated in Table 1, the addition of copolymer at a mole ratio of2:3 acrylic acid to methacrylic acid and at an amount of 0.1 weightpercent provides the best copper removal rate and clearing of residualcopper with low dishing. The dishing results are an average of stepheight ASH results for center and edge position at 90% and 100 um on a200 mm Sematech 854 mask TEOS wafer. Although some residual copper wasfound on most samples, the clear times were all less than 30 seconds.

1. A method for polishing of a semiconductor wafer, the semiconductorwafer having copper interconnect metal and residual copper, comprisingsteps of: contacting the wafer with a polishing composition, thepolishing composition comprising oxidizer, 0 to 1% by weight abrasive,copper inhibitor for the interconnect metal, 0.01 to 15% by weightcopper complexing agent, the complexing agent being selected from aceticacid, citric acid, glycolic acid, lactic acid, malic acid, oxalic acid,salicylic acid, succinic acid, tartaric acid, thioglycolic acid,glycine, alanine, aspartic acid, ethylene diamine, trimethyl diamine,malonic acid, gluteric acid, 3-hydroxybutyric acid, propionic acid,phthalic acid, isophthalic acid, 3-hydroxy salicylic acid, 3,5-dihydroxysalicylic acid, gallic acid, gluconic acid, pyrocatechol, pyrogallol,tannic acid, including salts and mixtures thereof, sodium diethyldithiocarbamate, ethyl acetoacetate and mixtures thereof, 0.01 to 5% byweight modified cellulose, the modified cellulose having carboxylic acidfunctionality and a molecular weight between 1K and 250K, 0.01 to 5% byweight copolymer of acrylic acid and methacrylic acid, and balancewater, wherein the copolymer of acrylic acid and methacrylic acid has amonomer ratio (acrylic acid/methacrylic acid) in the range of 1:9 to 9:1and the copolymer has a molecular weight in the range of 1K to 1000K;and clearing residual copper from the wafer with a polishing pad and themodified cellulose and copolymer of the polishing composition withoutexcessive dishing of the copper interconnect metal wherein clearing timefor clearing residual copper from the wafer is less than thirty seconds.2. The method of claim 1 wherein the copolymer of acrylic acid andmethacrylic acid has a monomer ratio (acrylic acid/methacrylic acid) ofabout 2:3.
 3. The method of claim 1 wherein the copolymer has amolecular weight in the range of 20K to 200K.
 4. The method of claim 1wherein the modified cellulose is water soluble cellulose modified withcarboxylic acid functionality from the group consisting of carboxymethyl cellulose, agar gum, arabic gum, ghatti gum, karaya gum, guargum, pectin, locust bean gum, tragacanth gums, tamarind gum, carrageenangum, and xantham gum, modified starch, alginic acid, mannuronic acid,guluronic acid, and their modifications, copolymers, and mixtures. 5.The method of claim 4 wherein the modified cellulose is carboxy methylcellulose.
 6. The method of claim 1 wherein the composition is abrasivefree.
 7. A method for polishing of a semiconductor wafer, thesemiconductor wafer having copper interconnect metal and residualcopper, comprising steps of: contacting the wafer with a polishingcomposition, the polishing composition comprising oxidizer, 0 to 1% byweight abrasive, copper inhibitor for the interconnect metal, 0.01 to15% by weight copper complexing agent, the complexing agent beingselected from acetic acid, citric acid, glycolic acid, lactic acid,malic acid, oxalic acid, salicylic acid, succinic acid, tartaric acid,thioglycolic acid, glycine, alanine, aspartic acid, ethylene diamine,trimethyl diamine, malonic acid, gluteric acid, 3-hydroxybutyric acid,propionic acid, phthalic acid, isophthalic acid, 3-hydroxy salicylicacid, 3,5-dihydroxy salicylic acid, gallic acid, gluconic acid,pyrocatechol, pyrogallol, tannic acid, including salts and mixturesthereof, sodium diethyl dithiocarbamate, ethyl acetoacetate and mixturesthereof, 0.01 to 5% by weight carboxy methyl cellulose and a molecularweight between 1K and 250K, 0.01 to 5% by weight copolymer of acrylicacid and methacrylic acid, and balance water, wherein the copolymer ofacrylic acid and methacrylic acid has a monomer ratio (acrylicacid/methacrylic acid) in the range of 1:9 to 9:1 and the copolymer hasa molecular weight in the range of 20K to 200K; and clearing residualcopper from the wafer with a polishing pad and the carboxy methylcellulose and copolymer of the polishing composition without excessivedishing of the copper interconnect metal wherein clearing time forclearing residual cooper from the wafer is less than thirty seconds. 8.The method of claim 7 wherein the polishing composition is abrasivefree.
 9. The method of claim 7 wherein the copolymer of acrylic acid andmethacrylic acid has a monomer ratio (acrylic acid/methacrylic acid) ofabout 2:3.